Articles coated with wear-resistant titanium compounds

ABSTRACT

A wear resistant coating on ceramic or metallic substrates is provided by coating the substrate with a titanium based alloy and then converting the titanium to titanium carbide, titanium nitride, titanium carboxynitride or titanium boride.

TECHNICAL FIELD

This relates to articles having a wear resistant coating. Moreparticular it relates to articles having a metallic or ceramic substrateand a coating comprising a hard titanium compound and another metal.

BACKGROUND

Various methods have been used to coat substrates with various titaniumcompounds. In U.S. Pat. Nos. 3,874,900 and 4,239,536 processes aredisclosed for providing a wear resistant surface of titanium carbide andtitanium nitride by a chemical vapor deposition process. In the chemicalvapor deposition process, titanium tetrachloride is reacted with eitherammonia or nitrogen to form titanium nitride. By use of the samechemical vapor deposition process, titanium tetrachloride is reactedwith a volatile hydrocarbon such as methane to form a coating oftitanium carbide. In the aforementioned patent these are combined togive a composite of titanium carbide and titanium nitride coating.

U.S. Pat. No. 3,868,235 also discloses a process for providing a hardsurface. In that process, a metal matrix having a melting point around2000° F. such as a nickel-chrome-ferrous alloy is applied to a substratein molten form thereafter a volatile non-metallic organic adhesive isapplied to the matrix. Hard metallic carbide such as titanium carbide isdeposited on the adhesive layer and the substrate is baked in a furnacebelow the melting point of the substrate and above the melting point ofthe matrix alloy whereby the adhesive is volatized, the matrix alloymelts and is bound to the carbide particles and the substrate.

Other processes which can be used to deposit hard compounds of titaniumon substrates include sputtering and flame or plasma sprayingtechniques. Illustrative of these processes are those disclosed in U.S.Pat. Nos. 3,779,720, and 3,895,156.

Chemical vapor deposition processes require use of titaniumtetrachloride, a difficult to handle chemical. The process as disclosedin U.S. Pat. No. 3,868,235 requires the use of an organic adhesive whichis evolved during processing thus adding a coat to the coated article.Sputtering, plasma, or flame spraying all require special equipment. Inaddition, plasma or flame spray coating require grinding to get an evencoating.

SUMMARY OF THE INVENTION

In accordance with one aspect of this invention there is provided aprocess for providing a relatively uniform coating containing arefractory titanium compound comprising brazing a preformed alloyconsisting essentially of from about 5 to about 30% by weight of nickel,from 0 to about 25% by weight of copper, balance titanium to a ceramicor metallic substrate. Thereafter, the titanium at the outer surface ofsaid alloy is converted to a refractory material selected from the groupconsisting titanium carbide, titanium nitride, titanium carboxynitride,titanium boride and mixtures thereof.

In accordance with another aspect of this invention, there is provided aprocess comprising forming a powder mixture consisting essentially offrom about 5% to about 30% by weight of nickel, from 0 to 25% by weightof copper, from about 0 to 35% by weight of tungsten carbide and balancetitanium hydride. Thereafter a ceramic or metallic substrate is coatedwith the powder and then heated in a vacuum to a temperature of about300° C. to about 400° C. for a sufficient time to convert the titaniumhydride to titanium metal. The coated substrate is then heated to 1050°C. to form a low melting temperature titanium-nickel copper alloy whichwill wet ceramic or metal substrate along with tungsten carbide. Thetitanium metal is then converted to a refractory material selected fromthe group consisting of titanium nitride, titanium carbide, titaniumcarboxynitride, titanium boride and mixtures thereof.

In another aspect of this invention there is provided an articleconsisting essentially of a ceramic or metallic substrate and a coatingcovering said substrate, said coating having an outer surface consistingessentially of from about 3 to about 27% by weight of nickel, from 0 toabout 24% by weight of copper, and the balance selected from titaniumcarbide, titanium nitride and titanium carboxynitride.

In still another aspect of this invention there is provided an articleconsisting essentially of a ceramic or metallic substrate, having acoating thereon. weight of copper, balance titanium. The outer coatingsurface of said coating consists essentially of from about 0 to about21.5% copper, from about 4.75% to about 31% by weight of nickel borideand balance titanium boride.

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above description of some of the aspects of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention uses the method of depositing or convertingtitanium metal in an alloy form to a hard titanium compound withthickness from 25 to 200 micron thickness, with a tough intermediatemetallurgical layer between the substrate and the hard titaniumcompound. A typical alloy with a flow temperature of 975° C. to 1050° C.is a material sold under the tradename of Ticuni by GTE Wesgo Divisionof GTE Products Corporation, Belmont, Calif. This material has acomposition of about 70% Ti and 15% by weight of Cu and 15% by weight ofNi. An additional material having a composition of about 30% nickel and70% titanium is useful in the practice of the present invention. Thealloys mentioned above can also be used as a powder mix. The abovealloy, Ticuni, can be prepared as a composite system with acopper-nickel alloy between inner and outer layers of titanium as shownin U.S. Pat. No. 3,652,237. As is shown in that patent the layers willmelt upon brazing to form the appropriate titanium-copper-nickel alloy.

The titanium alloy upon melting on a substrate will develop a gradientof elemental concentration based on substrate chemistry, temperature andtime. The treatment of above alloy at from about 900° C. to about 1100°C. with 99.9% pure methane will convert titanium to titanium carbide butthe carbide concentration gradient will decrease from the surface downwith intermediate form between the substrate and the formed carbidelayer close to the substrate the titanium will not be converted totitanium carbide. The intermediate zone will show high toughness andprevent spalling off of hard carbide dispersed layers.

The melted titanium alloy can be cooled to room temperature, coated withcarbon or packed in carbon and heated at from about 1000° to about 1100°C. in vacuum of 10⁻⁴ mm Hg for a few hours to produce titanium carbide.

A mixture of TiH₄ and Ni powder in a ratio of 70:30% (by weight) can bemixed and spray dried with a small quantity of polyvinyl alcohol binder.By feeding above powder through plasma gun with methane gas and inertgas, the molten alloy will react with the methane gas and form TiC plusnickel. The nickel will act as a binder to hold TiC material. Titaniumand nickel will alloy to form ceramic and metal wetting system to form astrong adhering layer.

An additional method of forming a hard titanium compound is by melting70% Ti-30% Ni alloy onto a steel substrate in a vacuum, remove fromvacuum and immerse in, a conventional boriding salt bath set at about850° C. for about 2 hours. The boriding treatment will convert bothnickel and titanium to the respective borides, both very hard materials.

The unique property of the Ti-Ni and Ti-Ni-Cu alloy systems is that theywill wet both metal and non-metallic surfaces such as alumina, siliconnitride, tungsten carbide, tantalum nitride, tantalum carbide,molybdenum carbide, diamond and the like. This capability to wet nearlyall surfaces means that titanium alloy can be used to hold the hardrefractory materials listed above onto the substrate material of eitherceramic or metallic surfaces, and followed by treatment to form theaforementioned hard compounds.

In order to more fully describe the subject invention, the followingdetailed examples are presented.

EXAMPLE 1

A porous alumina ceramic grinding wheel face is carefully coated with aslurry mixture of TiH₄ -49%, Ni-21%, WC-30% and glycerol, dried andheated to about 1050° C. under about 10⁻⁴ mm Hg vacuum. Thetitanium-nickel alloy will wet both alumina and tungsten carbide andbond tungsten carbide to the surface of alumina wheel. The titaniumportion is converted to titanium carbide, titanium nitride or titaniumcarboxynitride by the vapor reaction method heretofore described or totitanium boride by the boride bath procedure.

EXAMPLE 2

A paste is prepared using a mixture of 70% titanium hydride and 30%nickel powder mixed with glycerol. The paste is applied to an aluminasubstrate and melted at about 1000° C. to about 1100° C. in 10⁻⁴ mm Hgvacuum and then cooled. The melted alloy yields a coating of about 1-5mil thickness. The coating alloy, the substrate, is treated in thepreviously described manner to form the aforementioned hard titaniumcompound selected from titanium nitride, titanium carbide, titaniumcarboxynitride or titanium boride.

EXAMPLE 3

The following powder mix is prepared:

49%--Ti H₄

21%--Ni

30%--WC

The powder is mixed with glycerol to form a paste and applied to form acoating on the wear area of ceramic or metal component. It is thereafterheated to about 1000° C. to about 1100° C. in 10⁻⁴ mm Hg vacuum or invery dry (-100° C. dew point) inert gas to melt and flow the alloy. Thefinished product is coated with an abrasion resisting coating and can bemade even harder by converting the titanium to a hard titanium compoundsuch as titanium nitride, titanium carbide and the like.

EXAMPLE 4

A mixture of about 10% copper, about 63% TiH₄ and about 27% nickel, allin a form of a powder, is made into a paste and applied on a steelsubstrate. The assembly of the substrate and paste is placed in a vacuumfurnace, which is evacuated to about 10⁻⁴ to 10⁻⁵ mm Hg and heated toabout 1050° C. After about 5 minutes the material is nitriding at 900°to 1000° C. using anhydrous ammonia. The titanium is converted totitanium nitride.

EXAMPLE 5

A 5 mil thickness layer of a composite consisting of Ti 35%--CuNi30%--Ti 35% is placed on a surface of steel substrate. The assembly ofthe substrate and composite is placed in a vacuum furnace. The furnaceis evacuated to about 10⁻⁵ mm Hg and then heated to 1000° C. to 1050° C.to melt the composite on the steel. The furnace is cooled to about 900°C.-950° C. and methane gas is introduced to form titanium carbide.

EXAMPLE 6

A 20 mil thick layer of a composite consisting of Ti 35%--Ni 30%--Ti 35%is placed on a steel substrate and melted in a 10⁻⁵ mm Hg vacuum byheating to about 1050° C. The coated substrate is cooled to between 900°C. to 950° C. and the furnace is back filled with anhydrous ammonia gasto about 300 mm Hg to form TiN on the surface of the coated assembly.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:
 1. An article of manufacture consisting essentiallyof a substrate selected from ceramic and metallic substrates and acoating over at least a portion of said substrate said coating having anouter surface consisting essentially of from about 3% to about 27%nickel, from about 0 to about 24% by weight of copper and balanceselected from the group consisting of titanium carbide, titaniumnitride, titanium carboxynitride and mixtures thereof, an inner surfaceadjacent and bonded to said substrate said inner surface consistingessentially of from about 5% to about 30% by weight of nickel, from 0 toabout 25% by weight of copper, balance titanium, said inner and outersurfaces having been formed from the same brazing alloy composition anda zone between said outer and inner surface containing a gradient ofelemental concentration intermediate between said outer and said innersurfaces.
 2. An article of manufacture consisting essentially of asubstrate selected from ceramic and metallic substrates and a coatingover at least a portion of said substrate, said coating consistingessentially of an outer surface consisting essentially of from 0 toabout 21.5% by weight of copper, from about 4.75% to about 31% by weightof nickel boride, balance titanium boride and an inner surface bonded tosaid substrate said inner surface consisting essentially of from 0 to25% by weight of copper, from about 5% by weight to about 30% by weightof nickel, balance titanium, said inner and outer surfaces having beenformed from the same brazing alloy composition and a zone between saidinner and outer surfaces containing a gradient of elementalconcentration intermediate between said inner and outer surfaces.